1. Field of the Invention
This invention relates to a heat exchanger assembly for cooling an electronic device.
2. Description of the Prior Art
The operating speed of computers is constantly being improved to create faster computers. With this, comes an increase in heat generation and a need to effectively dissipate that heat.
Heat exchangers and heat sink assemblies have been used that apply natural or forced convection cooling methods to dissipate heat from electronic devices that are highly concentrated heat sources such as microprocessors and computer chips; however, air has a relatively low heat capacity. Thus, liquid-cooled units called LCUs employing a cold plate in conjunction with high heat capacity fluids have been used to remove heat from these types of heat sources. Although, LCUs are satisfactory for moderate heat flux, increasing computing speeds have required more effective heat sink assemblies.
Accordingly, thermosiphon cooling units (TCUs) have been used for cooling electronic devices having a high heat flux. A typical TCU absorbs heat generated by the electronic device by vaporizing a working fluid housed on the boiler plate of the unit. The boiling of the working fluid constitutes a phase change from liquid-to-vapor state and as such the working fluid of the TCU is considered to be a two-phase fluid. Vapor generated during boiling of the working fluid is then transferred to a condenser, where it is liquefied by the process of film condensation over the condensing surface of the TCU. The heat is rejected into ambient air flowing over the condenser and fins are commonly employed on the condenser to increase the heat transferred from the vapor. The condensed liquid is returned back to the boiler plate by gravity.
An example of such thermosiphons include U.S. Pat. No. 6,840,311 to Ghosh et al. The Ghosh patent discloses a heat exchanger assembly including a tube having a evaporation region extending between, and in fluid communication with, sealed first and second condensation regions. The tube includes internal fins extending from the tube's outer upper and/or lower surfaces into the evaporation and condensing regions. Each of the condensation regions has two portions, extending upwardly at different angles. A working fluid flows from the evaporation region to the condensation regions and back, as a result of the changing states.
Space or volume is at a premium in computer environments and it is essential that such thermosiphons maximize heat transfer while minimizing the space occupied. In addition to minimal space, it is desirable that the thermosiphon be relatively inexpensive to fabricate. The cost of fabrication is relatively high when the thermosiphon is fabricated from especially dedicated and unique components as distinguished from being fabricated from stock materials. Although the prior art effectively dissipates heat from electronic devices, there is a continuing need for alternative designs for effectively dissipating heat in a minimum of space while remaining relatively inexpensive to fabricate.